The invention relates to an arrangement for adjusting an electromagnetic actuator for a gas exchange valve, which includes valve opening and valve closing magnets between which an armature is movably disposed and held by upper and lower pretensioned valve springs, when the magnets are de-energized, in a rest position which is adjustable depending on sensor values of the magnets.
Electromagnetic actuators for the actuation of gas change valves (intake and exhaust valves) include generally two operating magnets, an opening magnet and a closing magnet with spaced pole faces, between which an armature is disposed movably with respect to the axis of the gas change valve. The armature acts on the valve shaft of the gas change valve either directly or by way of an armature bolt. In actuators operating in accordance with the principle of a mass oscillator, a pretensioned spring mechanism acts on the armature. Generally two pretensioned valve springs are used, that is, an upper and a lower valve spring. The upper valve spring applies a force to the gas change valve in an opening direction and the lower valve spring applies a force to the gas change valve in a valve closing direction.
When the magnets are de-energized, the armature is held by the springs in an equilibrium position between the magnets which, for best operation, is usually the center position between the pole surfaces of the magnets.
When, upon start-up, the actuator is operated, either the closing magnet or the opening magnet is shortly over-energized in order to pull the armature out of the equilibrium position, or an impulse application procedure is performed by which the magnets are alternately energized whereby the armature is oscillated until the armature can be caught by one of the magnets. When the gas change valve is closed, the armature is in contact with the pole surface of the energized closing magnet and is retained thereby. The closing magnet further pretensions the valve spring, which is effective in opening direction. To open the gas change valve, the closing magnet is de-energized and the opening magnet is energized. The valve spring acting in opening direction accelerates the armature beyond the equilibrium position so that it is attracted by the opening magnet. The armature is decelerated by the valve spring acting in the closing direction and hits the pole surface of the opening magnet by which it is held in an open valve position. To again close the gas change valve, the opening magnet is de-energized and the closing magnet is energized. The closing process corresponds to the opening process.
Certain values which are not originally taken into consideration or which change over time, such as manufacturing tolerances of the various components, heat expansion of different materials, different spring constants of the upper and the lower valve spring as well as settling of springs by aging could have the result that the equilibrium position determined by the valve springs does not coincide with the geometric center position between the pole surfaces or that it is not at a predetermined distance therefrom.
The energy required by the closing magnet and the opening magnet, called the catch energy, for attracting the armature from a predetermined distance increases exponentially with the distance. As a result, an armature which, in the rest position, is displaced from the center position for example in the direction toward the opening magnet, causes the energy requirement for the opening magnet to be reduced. At the same time, the energy requirements for the closing magnet are increased exponentially with the increased distance of the armature from the closing magnet that is at a substantially greater amount of energy is required for operating the opening magnet than for the closing magnet. As a result, the total energy requirement increases. The optimal equilibrium position of the armature determined by the valve spring is therefore the center position between the pole faces.
Furthermore, because of the exponential relationship, distances are rapidly reached for which the energy requirements are unacceptably high so that the opening or, respectively, closing magnet can no longer attract the armature. In this case, the actuator becomes inoperative.
DE 39 20 976 A1 discloses an electromagnetic control valve for displacement machines. It includes an armature which is held by at least two springs between an opening magnet and a closing magnet and operates in accordance with the principle of a spring-supported mass oscillator. For closing the control valve, the armature which acts on the shaft of the control valve is attracted by the closing magnet while pretensioning an opening spring. When the control valve opens, the closing magnet is de-energized and the opening spring, in cooperation with the energized opening magnet, moves the control valve to an open position.
By means of a control screw the equilibrium position of the oscillation system comprising the springs, the armature, the shaft of the control valve to be operated and a spring plate is so adjusted that the armature is disposed in the center between the closing and opening magnets when the magnets are de-energized. The center position, however, can be adjusted only when the valve is not in operation. Changes which may occur during operation of the valve, for example, because of different temperatures and heat expansion as well as by wear are not taken into account. In addition, it is difficult to determine accurately the center position during the adjustment.
DE 196 31 909 A1 discloses a method for the adjustment of the rest position of an armature of an electromagnetic actuator as it is used for example in piston type internal combustion engines for the operation of gas change valves. The rest position corresponds to an equilibrium position which is determined by the pretension of the valve springs while the magnets are de-energized. In this method, the inductivity of the two electromagnets is measured and, from a comparison of the two measured inductivity values, the location of the armature in the equilibrium position with respect to the pole faces of the electromagnets is derived. During measurement, the armature is in the equilibrium position. However it is also possible to measure the inductivity of the respective electromagnet, when it is engaged by the armature and to compare the measured valve and/or the difference between the two measured valves with a predetermined value and to derive, in this way, a correction value for a control signal. During measurement, the armature can be held in engagement with the respective electromagnet by mechanical means or by a holding current. Consequently, the method is not suitable to correct the center position or, respectively, the equilibrium position of the armature during operation of the system.
It is the object of the present invention to provide an arrangement and a method for adjusting the center position of an armature of an electromagnetic valve actuator during valve operation.